82 TRANSACTIONS, NATURAL HISTORY SOCIETY OK GLASGOW. 



Refemng to this mode of development and the possession by 

 Sigillaria of both rhizomes and roots, Renault says : — " It explains 

 also the difference of organization found in certain parts of these 

 organs.'" In describing a specimen he figures on PI. LXII., fig. 1, 

 he further says, " To the right of the figure one sees a young 

 branch bent at its extremity and on the \vay of elongation." - 



The figure to which he refers repi-esents what I presume he 

 regards as a rliizome arrived at the stage of producing an aerial 

 stem. If I am correct in this interpretation of his meaning, I 

 fail to see where the figure supports the contention. 



But we must remember that Renault believes that the rhizomes 

 also developed roots,'' and that these roots, which appeared sub- 

 sequently to the leaves, also added additional cicatrices to the 

 outer surface of the rhizome, and that this was a common, if not 

 constant, occurrence. Why, then, do specimens not show this? 

 They should be common. It is true Zeiller figures a specimen of 

 Stigmarla which shows on one side a greater number of cicatrices 

 than on the other side, * and these additional scars on one side of 

 the specimen he regards as those left by the roots. The mere 

 fact that at one part of the specimen a greater number of scars 

 occur than at another is no evidence that these additional scars 

 are those of roots. An absolute regularity in the arrangement or 

 number of the scars on the rhizomes cannot be expected in all 

 cases. Surely the root and leaf scars should show some difterence 

 in structure, but it is stated, " These two sorts of organs had, 

 however, the same exterior aspect, and they cannot be distin- 

 guished the one from the other on the imprint."^ If these two 

 organs, leaves and roots, have a similar exterior aspect, and when 

 removed from the rhizome leave behind scars indistinguishable from 

 each other, then we have in Stirjmaria a condition which exists 

 in no other plant, recent or fossil, with which I am acquainted. 



Functionally Stigmaria performs the duties of a root. I 

 believe of a root alone ; but from a true root it differs in the 



1 Renault, I.e., p. 549. 

 " I.e., p. 551. 



' Renault, "Etude sur les Stigmaria rhizomes et racines de iSigillaires,'" 

 Ann. de.i Sc. Giol, Vol. XII., pp. 23-24, ISSl. 



* Flore, foss. Bassin HouilUr d. Valenciennes, PI. XCI., figs. .3-4. 

 » Zeiller, I.e., p. 615. 



